The long-term goal of this research is to evaluate the interactive effects of environmental stressors and sodium chloride (NACl) and potassium (K) intake as they relate to hypertension development in a biracial population. In Study 1, 120 healthy men and women aged 20-49 years (60 black and 60 white individuals, with half of each racial subgroup having a positive (FH+) family history of hypertension) will each undergo 10 days on 4 counterbalanced dietary regimens: 1) free intake; 2) low NaCl/low K (25 mEq and 25 mEq/day); 3) high NaCl/low K (300 mEq and 25 mEq/day); and 4) high NaCl/high K (300 mEq and 175 mEq/day). On Day 9 of each diet, 24-hour ambulatory blood pressure monitoring will occur, and on Day 10, laboratory blood pressure, cardiac output and total peripheral resistance at rest and during two stressors (speech on a recent social conflict and forehead icepack) will be assessed. Plasma renin activity (PRA), aldosterone, and atrial natriuretic peptide (ANP) levels will be determined. On Day 11 of the high NaCl/low K and the high NaCl/high K diets, a 5-hour renal excretion protocol will occur involving urine collections every 30 min, to assess Na, K and fluid excretion along with hemodynamic adjustments occurring before, during and after an hour of competitive mental tasks. Psychosocial measures (anger-in, inhibition of negative emotions, job strain, maladaptive coping patterns, social conflict, work and home stress ratings, and social support) will be assessed as state and trait measures. "Salt sensitive" subjects will be defined as those who show decreases in baseline blood pressure from free diet to low NaCl/low K diet together with increases in pressure from low NaCl/low K to high NaCl/low K diets. "Slow stress natriuresis" subjects will be defined as those who fail to increase the rate of sodium excretion from baseline to stress hours on the high NaCl/low K diet. Hypotheses to be tested include: 1) both salt sensitivity and slow stress natriuresis will be more prevalent among blacks and FH+ subjects; 2)increasing K intake on the high NaCl diet will lower resting and stress blood pressures in salt sensitive subjects and diminish slow stress natriuresis. Study 2 will compare the effect of beta-blockade vs. combined alpha- and beta-blockade on renal excretion patterns during stress. Pilot Study 3 will assess the effect of a 4 month low NaCl/high K diet in reducing lab and ambulatory blood pressure and left ventricular mass in salt-sensitive subjects.